1. Field of the Invention
The invention relates to a tool utilized to remove particulate matter from perforations immediate formations in a subterranean well.
2. Description of the Prior Art
During the flow of production fluid into a well casing or while injecting secondary or tertiary recovery fluids into the formation, perforations in the well casing or the face of the producing formation may oftentimes become plugged with sand, silt, or other substances, restricting fluid flow between the formation of the casing bore. Heretofore, it has been common practice to utilize a valve apparatus which creates a high pressure differential to produce a sudden high velocity flow or surge of the formation fluid through the perforations and into the casing bore, thereby carrying sand, silt, and the like, into the tubing for subsequent elevation to the top of the well. As a result, the formation and perforations are washed or cleared, facilitating subsequent well production or the injection of secondary or tertiary recovery fluids into the formation.
Some of the prior art backsurge valving assemblies require drill or work string rotation to manipulate one or more of the valves. Such mechanically-activated manipulations may be undesirable in deviated holes and/or in wells of extreme depth. Moreover, some valving assemblies heretofore utilized in backsurge systems incorporate a diaphragm or disk-like element as a valve head which is ruptured by pressure, or is "cut" to open the valve, thus possible contributing to foreign particulate matter in the well which also could adversely affect subsequent operation of the valve assembly by becoming jammed between two moving parts.
Backsurge well-cleaning tools are known which are activated by pressure, one such tool being shown in U.S. Pat. No. 4,185,690, issued on Jan. 29, 1980 to the assignee of the present application. As disclosed therein, the backsurge tool generally comprises a tubing string having an upper normally closed valve communicating with a lower normally closed valve through an atmospheric pressure chamber. Although this backsurge well-cleaning tool is similar to the cleaning tool of the present invention in that it is activated by pressure, it includes a valve assembly having a blanking plug.